timer.c

   1 #include <avr/io.h>
   2 #include <avr/interrupt.h>
   3 #include <stdint.h>
   4 #include "timer.h"
   5
   6 uint16_t timer_count = 0;
   7
   8 // Configure timer 0 to generate a timer overflow interrupt every
   9 // 256*1024 clock cycles, or approx 61 Hz when using 16 MHz clock
  10 // This demonstrates how to use interrupts to implement a simple
  11 // inactivity timeout.
  12 void timer_init(void)
  13 {
  14     TCCR0A = 0x00;
  15     TCCR0B = 0x05;
  16     TIMSK0 = (1<<TOIE0);
  17 }
  18
  19 inline
  20 void timer_clear(void)
  21 {
  22     cli();
  23     timer_count = 0;
  24     sei();
  25 }
  26
  27 inline
  28 uint16_t timer_read(void)
  29 {
  30     uint8_t _sreg = SREG;
  31     uint16_t t;
  32
  33     cli();
  34     t = timer_count;
  35     SREG = _sreg;
  36
  37     return t;
  38 }
  39
  40 inline
  41 uint16_t timer_elapsed(uint16_t last)
  42 {
  43     uint8_t _sreg = SREG;
  44     uint16_t t;
  45
  46     cli();
  47     t = timer_count;
  48     SREG = _sreg;
  49
  50     return TIMER_DIFF(t, last);
  51 }
  52
  53 // This interrupt routine is run approx 61 times per second.
  54 // A very simple inactivity timeout is implemented, where we
  55 // will send a space character and print a message to the
  56 // hid_listen debug message window.
  57 ISR(TIMER0_OVF_vect)
  58 {
  59     timer_count++;
  60 }
  61